1. Field of the Invention
This invention relates generally to new immunomodulatory peptides and particularly to such peptides which have improved resistance to enzymatic degradation in the body.
2. Description of the Prior Art
U.S. Pat. Nos. 4,190,646 and 4,261,886 disclose various pentapeptides having activity similar to the long chain polypeptide known as thymopoietin described in U.S. Pat. Nos. 4,002,740 and 4,077,949. The above patents are all incorporated herein by reference. The biological activity of certain of these peptides is described in an article by M. E. Weksler, et al., J. Exp. Med. 148:996-1006 (1978). This article is also incorporated herein by reference. Published European Patent Application No. 25,897 and U.S. Pat. No. 4,361,673 also disclose various peptides asserted to have activity similar to thymopoietin. Thymopoietin III, also known as "splenin", is a similar peptide isolated from bovine spleen. Audhya, et al., Biochemistry, 20, 6195-6200 (1981). This material stimulates induction of both T cells and B cells.
Reference is made to the above-described patents, patent application, and articles for a discussion of other background material and the biological processes involved in the present invention.
Although these known peptides are useful for their immunomodulatory activity, they have been found to be rapidly destroyed by enzymes both in vitro and in vivo after administration to an animal or human recipient. See, for example, Int. J. Pept. and Protein Res., 14, 479-484 (1979); ibid, 22:187-193 (1983).
The present invention provides peptides and peptide compositions which are more resistant than the prior art peptides to enzymatic degradation in the body and hence are more therapeutically useful materials.